This research investigated whether number of siblings in the family facilitates theory of mind (ToM) understanding. A battery of tests was administered to measure ToM and VA (verbal ability) on 163 3.6 to 5.6 years-old children. No significant difference was found between ToM and number of siblings. In contrast, in a hierarchical multiple regression analysis, it was found out that, over and above age and VA, a significant contribution for birth order on ToM development was observed.